Method and device for controlling fan for cooling vehicle-mounted battery

ABSTRACT

A vehicle which uses an internal combustion engine and a motor generator as drive sources is provided with a battery disposed under a seat and a fan for cooling the battery. Power is exchanged between the motor generator and battery via an inverter. An electronic control unit estimates the level of background noise which is noise other than the operating sound of the fan in the passenger compartment based on the vehicle speed and rotation speed, etc., of the internal combustion engine. Then, the electronic control unit calculates an operation command value for the fan based on the estimated background noise level and temperature level of the battery and controls the rotation speed of the fan through the operation command value. As a result, it is possible to effectively cool the battery while reducing sensible noise caused by the operating sound of the fan.

This is a 371 of PCT/JP03/05270 filed 24 Apr. 2003, which claimspriority to Japanese Patent Application No. 2002-138755 filed 14 May2002, and JP 2003-070202 filed 14 Mar. 2003, the contents of which areincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for controllinga vehicle-mounted battery cooling fan.

BACKGROUND OF THE INVENTION

In recent years, electric cars using an electric motor as a drive sourceand hybrid cars using an electric motor and internal combustion engineas drive sources are attracting attention. These vehicles are normallyprovided with a chargeable battery and the electric motor is driven byelectric energy stored in this battery.

The battery includes internal resistance, and thereforecharging/discharging is accompanied by heat generation. For this reason,the temperature of the battery rises as charging/discharging of thebattery is repeated.

Furthermore, when such a battery is continuously used under ahigh-temperature condition, the life is generally shortened. For thisreason, to protect the battery, the battery may be controlled so as tolimit the charge/discharge current when the battery is under ahigh-temperature condition. However, in this case, sufficient propulsionmay not be obtained or in the case of a hybrid car, poor fuel efficiencyof the internal combustion engine may result.

For this reason, the above described vehicle is often provided with afan for cooling the battery. The rotation speed of the fan is normallyhigh when the battery is under a high temperature condition and slowunder a low temperature condition.

On the other hand, in the case of the hybrid car or the electric car,when the car is parked or when the electric motor is used as a drivesource, generally noise in the passenger compartment is often kept to alow level. When noise is at a low level in such a passenger compartment,if the fan is operating for cooling the battery, the operating sound ofthe fan increases relative to background noise in the passengercompartment, that is, noise other than the operating sound of the fan.Since passengers of the vehicle are rarely aware of the reason for theoperation of the fan under ordinary circumstances, the passengers feelthe operating sound of the fan as offensive to the ear.

Therefore, in order to reduce annoyance by the operating sound of thefan, the fan is stopped when, for example, the vehicle is parked and nooperating sound of the internal combustion engine is present.Alternatively, measures such as reducing the rotation speed of the fanare taken. For example, Japanese Laid-Open Patent Publication No.2001-103612 proposes a fan control apparatus for a hybrid car providedwith a function for reducing the rotation speed of the fan beforestopping idle operation when stoppage of the idle operation of theinternal combustion engine is predicted. As the fan control apparatusdisclosed in this publication, the rotation speed of the fan decreasesprior to the stoppage of idle operation, and therefore it is possible toreduce annoyance of the passengers caused by the operating sound of thefan while the idle operation is stopped.

However, it is not always possible to determine whether background noisein the passenger compartment, that is, noise other than the operatingsound of the fan is relatively small or not based only on whether theidle operation of the internal combustion engine is stopped or not. Thatis, even if the idle operation is stopped, background noise may be largein the passenger compartment due to sound other than the operating soundof the internal combustion engine. When the rotation speed of the fancontinues to be low for a long time though background noise in thepassenger compartment is relatively large, the temperature of thebattery increases and the life of the battery may be shortened.

In the case of not only a battery for supplying electric energy to avehicle motor, but also other vehicle-mounted batteries which realizecooling through rotation of the fan, the above described situation inwhich the operating sound becomes offensive to the ear is generallycommon.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a method andapparatus for controlling a vehicle-mounted battery cooling fan capableof effectively cooling the vehicle-mounted battery while reducingsensible noise due to operating sound of the fan.

In order to achieve the above described object, the present inventionprovides a method of controlling a fan for cooling a vehicle-mountedbattery. The vehicle is provided with a passenger compartment, and anelectric motor that functions as a drive source. The control methodcomprises a step of determining noise level in the passenger compartmentand a step of controlling an operation mode of the fan according to thedetermined noise level in the passenger compartment.

The present invention further provides an apparatus for controlling afan for cooling a vehicle-mounted battery. The vehicle is provided witha passenger compartment, and an electric motor that functions as a drivesource. The control apparatus comprises a determining means fordetermining noise level in the passenger compartment and controllingmeans for controlling the operation mode of the fan according to thedetermined noise level in the passenger compartment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a fan controlapparatus according to an embodiment of the present invention;

FIG. 2 is a flowchart showing a fan controlling procedure executed bythe fan control apparatus shown in FIG. 1;

FIG. 3 is a graph illustrating an operation command value for the fancalculated in the fan controlling procedure in FIG. 2;

FIG. 4 is a graph illustrating a relationship between an operationcommand value for the fan and background noise level;

FIG. 5 is a time chart showing a fan control procedure in anotherembodiment of the present invention; and

FIG. 6 is a flowchart showing a filtering processing procedureapplicable to another embodiment in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to FIG. 1 to FIG. 4, an embodiment of the presentinvention will be explained below.

As shown in FIG. 1, the fan control apparatus according to thisembodiment is applied to a vehicle using an internal combustion engine11 and an electric motor 12 as drive sources, that is, a hybrid car.This embodiment uses a synchronous motor as the electric motor 12. Thissynchronous motor also functions as a generator, and therefore theelectric motor 12 will be referred to as a motor generator (M/G) 12hereinafter. A seat 14 is provided for a passenger in a passengercompartment 13. A battery 15 is disposed under this seat 14 and electricenergy is exchanged between this battery 15 and M/G 12.

The vehicle moves when power generated by the internal combustion engine11 or M/G 12 is transmitted to an axle shaft 17 via a transmission 16.When the M/G 12 functions as a drive source, an inverter 18 converts DCelectric energy supplied from the vehicle-mounted battery 15 to AC andthe M/G 12 generates power using the AC electric energy. When aregenerative brake is applied to the driving vehicle, the driving forceof the axle shaft 17 is transmitted to the M/G 12 through thetransmission 16. The M/G 12 generates AC electric energy based on thedriving force of the axle shaft 17. The inverter 18 converts the ACelectric energy generated by the M/G 12 to DC and charges the battery15. Thus, the inverter 18 has the function of converting power from DCto AC and the function of converting power from AC to DC.

On the other hand, when the internal combustion engine 11 functions asthe drive source, power generated at the internal combustion engine 11is transmitted to the axle shaft 17 via the transmission 16 and at thesame time drives the M/G 12 as required to generate electric energy. Theinverter 18 converts AC electric energy generated by the M/G 12 to DCand charges the battery 15.

The vehicle is provided with an electronic control unit (ECU) 19 tocontrol the internal combustion engine 11 and M/G 12. This ECU 19 is acontroller made up of a microcomputer, etc., which provides the internalcombustion engine 11 with a command regarding opening of a throttlevalve (not shown) and a command regarding the amount of fuel injectionand at the same time monitors the engine operating state such as theengine rotation speed through various sensors (not shown). Furthermore,the ECU 19 gives the inverter 18 a switching command for the abovedescribed power conversion and monitors the operating condition such asthe rotation speed of the M/G 12 through various sensors (not shown).Furthermore, the ECU 19 calculates the vehicle speed based on the signalindicating the rotation speed of the axle shaft 17. Furthermore, the ECU19 controls an air-conditioner 20 mounted on the vehicle and monitorsthe state (opening) of a window 21 and state of a sound system 22(degree of volume adjustment).

When the vehicle is driving with power from the M/G 12, the battery 15discharges. Furthermore, when the regenerative brake is applied, kineticenergy of the vehicle is converted to electric energy through the M/G12, in which the electric energy is used to charge the battery 15.Therefore, when driving and stoppage of the vehicle are repeated, thebattery 15 repeats charging/discharging. Since internal resistanceexists in the battery 15, the battery 15 generates heat caused bycurrent flow accompanying charging/discharging. As described above, thetemperature rise of the battery 15 may cause shortening of the life ofthe battery 15 or degrades fuel efficiency of the internal combustionengine 11.

In order to prevent temperature rise of the battery 15, this vehicle isprovided with a fan 23 to cool the battery 15 in the passengercompartment 13. To control the operating mode of this fan 23 accordingto the temperature of the battery 15, the vehicle is provided with atemperature detector for detecting the temperature of the battery 15,that is, a temperature sensor 24. Furthermore, to control thecharging/discharging current of the battery 15 to a desired level, thevehicle is also provided with a sensor (not shown) for detecting avoltage and charging/discharging current of the battery 15. The ECU 19calculates a command value necessary to cool the battery 15 based on thedetected temperature, voltage and charging/discharging current andoutputs the command value to the fan 23. As a result, the fan 23 rotatesat a speed according to the command value, the air in the passengercompartment 13 is blown on the battery 15 and the battery 15 is cooled.

The operating sound of the fan 23 may constitute noise to passengers inthe passenger compartment 13. For example, when the vehicle is parkedand the operation of the internal combustion engine 11 is stopped, if noother noise source is present, the interior environment of the passengercompartment 13 is quiet. However, if the fan 23 is operating at thistime, the operating sound increases relative to the quiet environment ofthe passenger compartment 13, which causes the operating sound to becomeoffensive to the ear of the passengers. This noise becomes particularlynoticeable when the fan 23 is disposed under the passenger's seat 14 asin the case of this embodiment.

On the other hand, the acoustic environment in the passenger compartment13 is affected by not only the operating sound of the fan 23, but alsothe driving sound of the vehicle, operating sound of the internalcombustion engine 11, operating sound of the M/G 12, operating sound ofthe air-conditioner 20, opening of the window 21 and volume of the soundsystem 22. For example, when the vehicle is driving at high speed, whenthe rotation speed of the internal combustion engine 11 or M/G 12 ishigh, when the air-conditioner 20 is operating with high load, when thewindow 21 is fully open, or when the sound system 22 is operating withhigh sound volume, noise in the passenger compartment 13 naturallyincreases. In such a case, even if the operating sound of the fan 23 isrelatively large, sound other than the operating sound of the fan 23 islarge, and therefore the operating sound of the fan 23 relativelydecreases. Therefore, sensible noise of the fan 23 to the passengers ofthe vehicle is small.

Therefore, in order to reduce sensible noise with respect to this fan 23and effectively cool the battery 15, this embodiment is designed tocontrol the fan 23 as follows. Since this embodiment regards theoperating sound of the fan 23 as an evaluation target, sound caused byall noise sources other than the fan 23 is treated as background noise.Vehicle components assumed to constitute possible sources of thisbackground noise (causes for noise) are shown enclosed with adouble-line rectangle in FIG. 1. That is, as shown in FIG. 1, thisembodiment assumes the axle shaft 17 through which the vehicle speed isdetected, internal combustion engine 11, M/G 12, air-conditioner 20,window 21 and sound system 22 as the background noise source (causes forbackground noise).

The above described ECU 19 is provided with a background noiseestimation section 31, a fan operation command calculation section 32and a fan operation command output section 33 for effectively coolingthe battery 15 using the fan 23 according to background noise in thepassenger compartment 13. These elements (31 to 33) show the functionsexecuted by the ECU 19 according to a predetermined control program. TheECU 19 including these elements (31 to 33) controls the fan 23 accordingto the procedure shown in the flowchart in FIG. 2.

First, in step S201, the ECU 19 determines whether there is any requestfor special operation on the fan 23. This request for a specialoperation is made when the temperature of the battery 15 is recognizedto be abnormal or when the fan 23 or other parts have trouble. Whenthere is a request for a special operation, the ECU 19 goes to step S209and calculates a command value according to the special operation as thecommand value corresponding to the fan 23. The process in this step S209is defined as an abnormal process which is different from a normalprocess, which will be described later. For example, when the battery 15is abnormally hot, a process such as operating the fan 23 irrespectiveof background noise is performed.

On the other hand, when there is no request for a special operation, theECU 19 goes to step S202 and estimates the background noise level in thepassenger compartment 13 caused by the aforementioned background noisesource. The background noise level is estimated based on the commandvalue given from the ECU 19 to each background noise source or statusvalue of the background noise source detected by various sensors. Morespecifically, the level of the background noise in the passengercompartment 13 is estimated based on the vehicle speed obtained from therotation speed of the axle shaft 17, rotation speed of the internalcombustion engine 11, rotation speed of the M/G 12, command valuecorresponding to the air-conditioner 20, opening of the window 21 anddegree of adjustment of sound volume of the sound system 22. With regardto the level of background noise, it is possible to estimate noisecaused by each background noise source individually and determine thelevel of background noise comprehensively based on the estimation, forexample. Furthermore, in estimating the level of background noise, it ispreferable to consider relationships between a plurality of mutuallyaffecting factors such as the relationship between the vehicle speed andopening of the window 21. With regard to the process of this step S202,the ECU 19 functions as the background noise estimation section 31.

Then, in steps S203 to S207, the ECU 19 calculates an operation commandvalue for the fan 23 based on the estimated background noise level andtemperature of the battery 15 detected by the temperature sensor 24. Forthe processes in these steps S203 to S207, the ECU 19 functions as thefan operation command calculation section 32. More specifically, in stepS203, the fan operation command calculation section 32 determineswhether the specified background noise level satisfies a predeterminedfirst condition or not, that is, whether the background noise level isequal to or below a predetermined first threshold or not. When thebackground noise level satisfies the first condition, that is, equal toor below the first threshold, the fan operation command calculationsection 32 goes to step S205 a, sets the background noise level to “1”and stores the set background noise level in a memory (not shown)provided for the ECU 19. On the other hand, when the estimatedbackground noise level does not satisfy the first condition, that is,the estimated background noise level is greater than the firstthreshold, the fan operation command calculation section 32 goes to stepS204 and determines whether the background noise level satisfies apredetermined second condition or not, that is, whether the backgroundnoise level is equal to or below a second threshold which is greaterthan the first threshold.

When the background noise level satisfies the second condition, that is,the background noise level is equal to or below the second threshold,the fan operation command calculation section 32 goes to step S205 b,sets the background noise level to “2” and stores the set backgroundnoise level in the above described memory. On the other hand, when thebackground noise level does not satisfy the second condition, that is,the background noise level is greater than the second threshold, the fanoperation command calculation section 32 goes to step S205 c, sets thebackground noise level to “3” and stores the set background noise levelin the memory. A smaller value indicating the background noise levelmeans that the environment in the passenger compartment 13 is quieter,while a larger value indicating the background noise level means thatthe background noise level in the passenger compartment 13 is high.Thus, executing processes in steps S203 to S205 c, shows the estimatedbackground noise level with any one of background noise levels in aplurality of stages (3 stages in this embodiment).

After step S205 a, step S205 b or step S205 c, the fan operation commandcalculation section 32 sets the temperature level according to thetemperature of the battery 15 detected by the temperature sensor 24 instep S206 and stores the set temperature level in the memory. Thetemperature level is set to any one of temperature levels in five stages“A” to “E” according to the detected temperature of the battery 15. Thatis, the temperature of the battery 15 is indicated by any one oftemperature levels in a plurality of stages. The temperature levelindicates that the temperature of the battery 15 increases in order ofA, B, C, D and E. That is, the temperature level at “A” indicates thatthe temperature of the battery 15 is lowest and the temperature level at“E” indicates that the temperature of the battery 15 is highest. Next,in step S207, the fan operation command calculation section 32calculates an operation command value for the fan 23 based on thebackground noise level and temperature level set above.

In step S208, the ECU 19 outputs the calculated command value to the fan23. As a result, the fan 23 follows the command value or morespecifically the fan 23 is controlled so as to operate at a rotationspeed corresponding to the command value. In the process in this stepS208, the ECU 19 functions as the fan operation command output section33.

The command value calculated in step S207 is defined so as to have acharacteristic as illustrated in FIG. 3. That is, as shown in FIG. 3, asthe temperature level increases from “A” to “E” and as the backgroundnoise level increases from “1” to “3”, the command value for the fan 23increases. For example, when the background noise level is set to “1”,as shown in single-dot dashed line in FIG. 3, the command valueincreases stepwise from “0”→“0”→“0.5”→“1.5”→“2.5” as the temperaturelevel increases from “A” to “E”. Furthermore, when the background noiselevel is set to “2”, as shown in a solid line in FIG. 3, the commandvalue increases stepwise from “0”→“1”→“2”→“3”→“4” as the temperaturelevel increases from “A” to “E”. Furthermore, when the background noiselevel is set to “3”, as shown by the dotted line in FIG. 3, as thetemperature level increases from “A” to “E”, the command value increasesstepwise from “1”→“2”→“3”→“4”→“5”. The command value for the fan 23 is,for example, a voltage value itself, or a voltage whose duty ratio iscontrolled. As the command value increases (as the voltage or duty ratioincreases), the rotation speed of the fan 23 increases.

In this way, the command value for the fan 23 increases as thebackground noise level increases according to the temperature of thebattery 15 at that time. FIG. 4 is a graph illustrating the relationshipbetween the background noise level and command value for the fan 23 whenthe temperature level is set to “C”. As shown in this graph, when thetemperature level is set to “C”, the command value increases stepwisefrom “0.5”→“2”→“3” as the background noise level increases from“1”→“2”→“3”.

This embodiment explained so far has the following excellent advantages:

(1) The ECU 19 has the function of determining noise in the passengercompartment 13 and controlling the operating mode of the fan 23according to the determined noise. That is, the ECU 19 determines thenoise level in the passenger compartment 13 and calculates a commandvalue for the fan 23 according to the determined noise level. As thenoise level in the passenger compartment 13 increases, a greater commandvalue is calculated so as to rotate the fan 23 at a higher speed. Whenthe noise level in the passenger compartment 13 is lower, a smallercommand value is calculated so as to rotate the fan 23 at a lower speed.That is, the operating mode of the fan 23 is controlled according to thenoise level in the passenger compartment 13 so that the operating soundof the fan 23 becomes smaller when the acoustic environment in thepassenger compartment 13 is estimated to be quiet, and the battery 15 iseffectively cooled when the noise level in the passenger compartment 13is estimated to be large. As a result, it is possible to reduce sensiblenoise of the fan 23 to passengers in the passenger compartment 13 andeffectively cool the battery 15 as well.

(2) In controlling the fan 23, noise in the passenger compartment 13 tobe estimated is noise other than the operating sound of the fan 23, thatis, background noise for the operating sound of the fan 23. The level ofthe background noise is estimated based on the content of an operationcommand given to each of vehicle components that are estimated as causesfor background noise or the operating status of each vehicle component.For this reason, the level of background noise is estimated accuratelyand the fan 23 is operated at an exact rotation speed according to thelevel of the estimated background noise level. Furthermore, it is alsopossible to designate only the vehicle components selected beforehand asbackground noise factors as estimation targets of background noiselevels. For example, noise factors which should not be handled asbackground noise targets, such as conversation between passengers, canbe purposely excluded from the estimation targets.

(3) The battery 15 is cooled using the air in the passenger compartment13. For this reason, when the air in the passenger compartment 13 iskept to an appropriate temperature by the air-conditioner 20, thebattery 15 is cooled more stably compared to the case where the battery15 is cooled using the air outside the passenger compartment 13, whichdrastically changes.

(4) The ECU 19 calculates a command value for the fan 23 based on notonly noise in the passenger compartment 13 but also the temperature inthe battery 15. For this reason, while sensible noise of the fan 23 topassengers in the passenger compartment 13 is reduced, it is possible tocool the battery 15 more adequately according to the temperature. Sincean abnormal temperature rise of the battery 15 can be prevented, it ispossible to prevent the life of the battery 15 from being shortened.Furthermore, prevention of temperature rise of the battery 15 leads to adecrease in load on the internal combustion engine 11 and improvement offuel efficiency of the internal combustion engine 11.

(5) Causes for background noise can be the vehicle speed (that is, thevehicle itself), the internal combustion engine 11, the M/G 12, theair-conditioner 20, the window 21 and the sound system 22. These factorsfor background noise generally reflect factors for background noise inthe passenger compartment 13 of the hybrid car. For this reason, thebackground noise level in the passenger compartment 13 of the hybrid caris adequately estimated and the operation of the fan 23 is controlled inan appropriate manner.

(6) In a vehicle according to this embodiment, the battery 15 isdisposed under the seat 14 and the operating sound of the fan 23 iseasily sensed by the ears of passengers. Applying the fan controlaccording to this embodiment as described above to such a vehicle isfurther effective in reducing sensible noise of the fan 23 to thepassengers in the passenger compartment 13.

Another embodiment of the present invention will be explained centeredon differences from the embodiment in FIG. 1 to FIG. 4 according to FIG.5 and FIG. 6.

In the embodiment in FIG. 1 to FIG. 4, the amount of operation of thefan 23, that is, the rotation speed is changed according to thebackground noise level in the passenger compartment 13 and temperaturelevel of the battery 15. However, when the operating sound of the fan 23drastically changes due to change of rotation speed of the fan 23,passengers may feel a sense of discomfort. However, while a drasticincrease of the operating sound of the fan 23 causes passengers to feela noticeable sense of discomfort, a decrease of the operating sound ofthe fan 23 is less likely to cause passengers to feel a sense ofdiscomfort no matter how drastic the decrease may be.

Thus, this embodiment applies a filtering process to the operationcommand value calculated according to the fan controlling procedure inFIG. 2 for slowing the variation of the operation command value.Hereinafter, the operation command value calculated in the fancontrolling procedure in FIG. 2 will be referred to as a targetoperation command value St and the operation command value after thefiltering process will be referred to as a final operation command valueSfin.

In the filtering process, as shown in FIG. 5, the final operationcommand value Sfin input to the fan 23 with respect to one change of thetarget operation command value St is changed stepwise in a plurality ofstages. When the target operation command value St is increased so as toincrease the amount of operation of the fan 23, the final operationcommand value Sfin is increased by a predetermined amount of increase SIper predetermined unit time Δt. Furthermore, when the target operationcommand value St is decreased so as to reduce the amount of operation ofthe fan 23, the final operation command value Sfin is decreased by apredetermined amount of decrease S2 per predetermined unit time Δt. Theamount of increase S1 is set to a value sufficiently small relative tothe amount of decrease S2. For this reason, when the amount of operationof the fan 23 is increased, the final operation command value Sfin isslowly changed compared to when the amount of operation is decreased.

FIG. 6 is a flowchart showing the above described filtering processingprocedure. The filtering processing procedure is performed by the ECU 19following the fan controlling procedure in FIG. 2.

When this filtering processing procedure is started, first in step S601,the ECU 19 determines whether the target operation command value St isequal to or greater than the current final operation command value Sfinor not.

When the decision result in step S601 is positive, the ECU 19 goes tostep S610 and determines whether the difference (St−Sfin) between thetarget operation command value St and final operation command value Sfinis smaller than the above described amount of increase Si or not. Ifthis difference (St−Sfin) is equal to or greater than the amount ofincrease Si, the ECU 19 goes to step S611, sets the result of adding theamount of increase Si to the current final operation command value Sfinas a new final operation command value Sfin, and ends this process.Furthermore, when the difference (St−Sfin) is smaller than the amount ofincrease S1, the ECU 19 goes to step S612, sets the current targetoperation command value St as the final operation command value Sfin andends this process.

On the other hand, when the target operation command value St is smallerthan the current final operation command value Sfin in step S601, theECU 19 goes to step S620 and determines whether the difference (Sfin−St)between the final operation command value Sfin and target operationcommand value St is smaller than the amount of decrease S2 or not. Ifthe difference (Sfin−St) is equal to or greater than the amount ofdecrease S2, the ECU 19 goes to step S621, sets the result ofsubtracting the amount of decrease S2 from the current final operationcommand value Sfin as a new final operation command value Sfin and endsthis process. On the other hand, if the difference (Sfin−St) is smallerthan the amount of decrease S2, the ECU 19 goes to step S622, sets thecurrent target operation command value St as the final operation commandvalue Sfin and ends this process.

This embodiment explained so far has the following advantages inaddition to the advantages of the embodiment in FIG. 1 to FIG. 4.

(7) The operation command value for the fan 23 is changed gradually whenthe amount of operation of the fan 23 is changed. For this reason, theamount of operation of the fan 23, that is, the rotation speed slowlychanges without changing drastically. A gradual change of the rotationspeed of the fan 23 causes a gradual change in the operating sound ofthe fan 23. As a result, it is possible to reduce the sense ofdiscomfort that the change in operating sound of the fan 23 causes tothe passengers.

(8) The rate of change in the amount of operation of the fan 23 isdifferentiated when the amount of operation of the fan 23 is increasedand decreased. More specifically, when the amount of operation of thefan 23 is increased, the rate of change in the amount of operation islower than when the amount of operation of the fan 23 is decreased. Forthis reason, when the amount of operation of the fan 23 is increased,the drastic increase in the operating sound is suppressed and when theamount of operation of the fan 23 is decreased, the operating sound isspeedily decreased. As a result, it is possible to effectively reducethe sense of discomfort that the operating sound of the fan 23 causes tothe passengers.

The above described embodiments may be modified as follows.

In the filtering processing procedure shown in FIG. 6, the finaloperation command value Sfin is changed stepwise. However, it ispossible to gradually change the final operation command value Sfin inany mode, for example, continuously change the final operation commandvalue Sfin or change the change rate of the final operation commandvalue Sfin according to various conditions, etc.

The above described embodiments have enumerated the axle shaft 17through which the vehicle speed is detected, internal combustion engine11, M/G 12, air-conditioner 20, window 21 and sound system 22 as thevehicle components which can be considered as causes for backgroundnoise, but the present invention is not necessarily limited to thesevehicle components. All these vehicle components need not be assumed ascauses for background noise. It is also possible to assume vehiclecomponents other than these vehicle components, for example, a wiper forwiping away raindrops, an air cleaner provided in the passengercompartment, etc., as causes for background noise.

With respect to each of vehicle components to be estimated as causes forbackground noise, whether the operation command value for each elementshould be used to estimate the background noise level or the operatingcondition value of each element should be used to estimate thebackground noise level can be selected as appropriate within the rangein which the background noise level can be accurately estimated.

The location of the battery 15 is not limited to under the seat 14, butmay also be other than under the seat 14 in the passenger compartment 13or outside the passenger compartment 13.

Cooling of the battery 15 is not limited to cooling using the air in thepassenger compartment 13, but may also be performed using air outsidethe passenger compartment 13. The fan 23 may be placed inside thepassenger compartment 13 or may also be placed outside the passengercompartment 13.

The battery to be cooled by using the fan 23 is not limited to thebattery 15 which supplies power to the electric motor 12 that functionsas a drive source of the vehicle, but may also be any battery mounted onthe vehicle.

In the fan controlling procedure in FIG. 2, the temperature of thebattery 15 may be expressed with temperature levels of a plurality ofstages other than five stages or may be treated as a continuousnumerical value instead of temperature levels in a plurality of stages.Likewise, the background noise levels in the passenger compartment 13may also be expressed with levels in a plurality of steps other thanthree stages. The background noise levels may also be treated as acontinuous numerical value instead of levels in a plurality of stages.Furthermore, operation command values corresponding to the fan 23 arenot limited to values which vary stepwise and may also be a value whichvaries continuously.

Control of the fan 23 based on the temperature level may be performedindependently of control of the fan 23 based on the background noiselevel. Furthermore, instead of control of the fan 23 based on thetemperature level, it is also possible to perform control of only thefan 23 based on the background noise level.

It is possible to reduce a command value for the fan 23 to an extentthat the battery 15 is not adversely influenced if the passengercompartment 13 is in a quiet environment even if the detectedtemperature of the battery 15 is high. Thus, the fan 23 may becontrolled further considering temporal conditions in addition to thetemperature level and background noise level.

In addition to the background noise level estimated with a noise gauge41 provided on the vehicle as shown with a dotted line in FIG. 1, it isalso possible to determine the noise level in the passenger compartment13 by further taking into account the actual noise level directlymeasured using the noise gauge 41. Instead of estimating the backgroundnoise level, it is possible to control the fan 23 only based on theactual noise level as directly measured using the noise gauge 41. Inthis case, the noise gauge 41 functions as the determining means fordetermining the noise level in the passenger compartment 13. Using thedirectly measured actual noise level, it is possible to control the fan23 by reflecting the acoustic environment in the passenger compartment13 more faithfully. The noise gauge 41 may be placed inside thepassenger compartment 13 or may also be placed outside the passengercompartment 13.

It is also possible to provide a sound absorbing member or soundinsulator as appropriate to reduce the operating sound of the fan 23 orincrease the cross section of the passage for the cooling air to be sentto the battery 15.

The present invention is not limited to a hybrid car provided with aninternal combustion engine 11 and M/G 12, but is also applicable to anelectric car. Such an electric car may be provided with a secondarybattery or fuel cell as the battery and a motor operating based on powerof the battery as the drive source.

1. A method of controlling a fan for cooling a vehicle-mounted battery,said vehicle being provided with a passenger compartment for passengersand an electric motor which functions as a drive source of the vehicle,said control method comprising: determining noise level in saidpassenger compartment; and outputting a command value to control arotational speed of said fan according to the determined noise level inthe passenger compartment so that the fan is rotated at a higher speedas the determined noise level increases, wherein said control of therotational speed of the fan includes differentiating a rate of change ofthe rotational speed of the fan so that the rate of change is lower whenthe rotational speed is increased than when decreased.
 2. The controlmethod according to claim 1, wherein said determining noise level insaid passenger compartment includes estimating background noise leveldue to noise other than noise generated from said fan.
 3. The controlmethod according to claim 2, wherein said background noise level isestimated based on the content of an operation command corresponding toat least one vehicle component.
 4. The control method according to claim2, wherein said background noise level is estimated based on thecondition of at least one vehicle component.
 5. The control methodaccording to claim 2, wherein noise level in said passenger compartmentis determined based on estimated background noise level in the passengercompartment and an actually measured noise level in the passengercompartment.
 6. The control method according to claim 1, wherein saiddetermining noise level in the passenger compartment includes actuallymeasuring the noise level in the passenger compartment.
 7. The controlmethod according to claim 1, further comprising detecting thetemperature of said battery, wherein the rotation state of said fan iscontrolled according to the detected battery temperature.
 8. Anapparatus for controlling a fan for cooling a vehicle-mounted battery,said vehicle being provided with a passenger compartment for passengersand an electric motor which functions as a drive source of the vehicle,said control apparatus comprising: determining means for determiningnoise level in said passenger compartment; and controlling means foroutputting a command value to control a rotational speed of said fanaccording to the determined noise level in the passenger compartment sothat the fan is rotated at a higher speed as the determined noise levelincreases, wherein said controlling means includes differentiating arate of change of the rotational speed of the fan so that the rate ofchange is lower when the rotational speed is increased than whendecreased.
 9. The control apparatus according to claim 8, wherein saiddetermining means estimates background noise level which is noise otherthan noise generated from said fan and determines noise level in saidpassenger compartment based on the estimated background noise level. 10.The control apparatus according to claim 9, wherein said determiningmeans estimates background noise level in said passenger compartmentbased on a content of an operation command corresponding to at least onevehicle component.
 11. The control apparatus according to claim 9,wherein said determining means estimates background noise level in saidpassenger compartment based on a condition of vehicle components thatcan be causes for said background noise level.
 12. The control apparatusaccording to claim 10, wherein said at least one vehicle componentincludes at least one of said electric motor, air-conditioner, window,sound system, and a member through which vehicle speed can be detected.13. The control apparatus according to claim 10, wherein said vehicle isprovided with an internal combustion engine which functions as a drivesource in addition to said electric motor and said vehicle componentsinclude at least one, said electric motor, said internal combustionengine, air-conditioner, window, sound system, and a member throughwhich vehicle speed can be detected.
 14. The control apparatus accordingto claim 9, further comprising a noise gauge for directly measuringnoise level in said passenger compartment, wherein said determiningmeans determines noise level in said passenger compartment based on theestimated background noise level in the passenger compartment and themeasured noise level in the passenger compartment.
 15. The controlapparatus according to claim 8, wherein said determining means comprisesa noise gauge for directly measuring noise level in said passengercompartment and said controlling means controls the rotation state ofsaid fan based on the measured noise level in the passenger compartment.16. The control apparatus according to claim 8, wherein said fan blowsthe air in said passenger compartment on the battery to cool saidbattery.
 17. The control apparatus according to claim 8, wherein saidbattery is disposed under a seat provided in said passenger compartment.18. The control apparatus according to claim 8, further comprising atemperature detector which detects the temperature of said battery,wherein said controlling means controls the rotation state of said fanaccording to the determined noise level in the passenger compartment andthe detected temperature of the battery.
 19. An apparatus forcontrolling a fan for cooling a vehicle-mounted battery, said vehiclebeing provided with a passenger compartment for passengers and anelectric motor which functions as a drive source of the vehicle, saidcontrol apparatus comprising: determining logic for determining noiselevel in said passenger compartment; and controlling logic foroutputting a command value to control a rotational speed of said fanaccording to the determined noise level in the passenger compartment sothat the fan is rotated at a higher speed as the determined noise levelincreases, wherein said controlling logic differentiates a rate ofchange of the rotational speed of the fan so that the rate of change islower when the rotational speed is increased than when decreased.